1. Field of the Invention
The present invention relates to a knock determining apparatus for an internal combustion engine.
2. Description of Related Art
In general, a knock determining apparatus for an internal combustion engine includes a knock sensor, which is installed in a cylinder block of the internal combustion engine to sense knock vibrations. A knock frequency component is extracted from an output signal of the knock sensor through a band-pass filter. In one exemplary case, peak values of the knock frequency component are compared with a corresponding knock determination threshold value to determine whether the knock is present. In another exemplary case, measured output values of knock frequency component in a predetermined period are integrated, and the integrated value is compared with a corresponding knock determination threshold value to determine whether the knock is present.
The generation of the knock may be limited or alleviated by retarding the ignition timing. However, when the ignition timing is retarded, the engine output power and the fuel consumption are deteriorated. Thus, it is required to advance the ignition timing within a permissible auditory knock sound range to improve the engine output power and the fuel consumption. Thus, the knock determination threshold value needs to be a value, which enables detection of only the certain knocks, which have a level that exceeds a permissible auditory level.
In view of the above points, as recited in Japanese Examined Patent Publication No. H06-60621 (corresponding to U.S. Pat. No. 4,617,895 and U.S. Pat. No. 4,711,214), it is known to correct the knock determination threshold value in such a manner that a distribution of logarithmically transformed values of the peak values of the output signal of the knock sensor have a predetermined shape or profile.
However, when noise (e.g., injection noise of a direct injection engine), which is larger than the knock vibrations, is constantly overlapped with the sensor output, the constant noise could be possibly erroneously determined as the knock vibrations, and thereby the knock determination accuracy is disadvantageously deteriorated under the presence of the noise generation.